1
LT1372/LT1377
500kHz and 1MHz
High Efficiency
1.5A Switching Regulators
s
Boost Regulators
s
CCFL Backlight Driver
s
Laptop Computer Supplies
s
Multiple Output Flyback Supplies
s
Inverting Supplies
APPLICATIO
N
S
U
The LT
1372/LT1377 are monolithic high frequency
switching regulators. They can be operated in all standard
switching configurations including boost, buck, flyback,
forward, inverting and "Cuk." A 1.5A high efficiency switch
is included on the die, along with all oscillator, control and
protection circuitry. All functions of the LT1372/LT1377
are integrated into 8-pin SO/PDIP packages.
The LT1372/LT1377 typically consumes only 4mA quies-
cent current and has higher efficiency than previous parts.
High frequency switching allows for very small inductors
to be used. All surface mount components consume less
than 0.5 square inch of board space.
New design techniques increase flexibility and maintain
ease of use. Switching is easily synchronized to an exter-
nal logic level source. A logic low on the shutdown pin
reduces supply current to 12
A. Unique error amplifier
circuitry can regulate positive or negative output voltage
while maintaining simple frequency compensation tech-
niques. Nonlinear error amplifier transconductance re-
duces output overshoot on start-up or overload recovery.
Oscillator frequency shifting protects external compo-
nents during overload conditions.
DESCRIPTIO
N
U
s
Faster Switching with Increased Efficiency
s
Uses Small Inductors: 4.7
H
s
All Surface Mount Components
s
Only 0.5 Square Inch of Board Space
s
Low Minimum Supply Voltage: 2.7V
s
Quiescent Current: 4mA Typ
s
Current Limited Power Switch: 1.5A
s
Regulates Positive or Negative Outputs
s
Shutdown Supply Current: 12
A Typ
s
Easy External Synchronization
s
8-Pin SO or PDIP Packages
FEATURES
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
N
U
12V Output Efficiency
OUTPUT CURRENT (A)
0.01
50
EFFICIENCY (%)
60
70
80
90
0.1
1
LT1372 TA02
100
V
IN
= 5V
5V-to-12V Boost Converter
LT1372/LT1377
V
IN
V
C
5V
1
2
8
5
4
6, 7
GND
FB
LT1372 TA01
V
SW
S/S
L1*
4.7
H
C1**
22
F
C4**
22
F
C2
0.047
F
C3
0.0047
F
R3
2k
R2
6.19k
1%
R1
53.6k
1%
V
OUT
12V
D1
MBRS120T3
ON
OFF
*COILCRAFT DO1608-472 (4.7
H) OR
COILCRAFT DT3316-103 (10
H) OR
SUMIDA CD43-4R7 (4.7
H) OR
SUMIDA CD73-100KC (10
H) OR
**AVX TPSD226M025R0200
L1
4.7
H
10
H
I
OUT
0.25A
0.35A
MAX I
OUT
+
+
2
LT1372/LT1377
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
W
U
U
PACKAGE/ORDER I FOR ATIO
Consult factory for Military grade parts.
Supply Voltage ....................................................... 30V
Switch Voltage
LT1372/LT1377 .................................................. 35V
LT1372HV .......................................................... 42V
S/S Pin Voltage ....................................................... 30V
Feedback Pin Voltage (Transient, 10ms) ..............
10V
Feedback Pin Current ........................................... 10mA
Negative Feedback Pin Voltage
(Transient, 10ms) .............................................
10V
Operating Junction Temperature Range
Commercial ........................................ 0
C to 125
C*
Industrial ......................................... 40
C to 125
C
Short Circuit ......................................... 0
C to 150
C
Storage Temperature Range ................ 65
C to 150
C
Lead Temperature (Soldering, 10 sec) ................. 300
C
ORDER PART NUMBER
LT1372CN8
LT1372HVCN8
LT1372CS8
LT1372HVCS8
LT1372IN8
LT1372HVIN8
LT1372IS8
LT1372HVIS8
LT1377CS8
LT1377IS8
1
2
3
4
8
7
6
5
TOP VIEW
V
C
FB
NFB
S/S
V
SW
GND
GND S
V
IN
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125
C,
JA
= 100
C/ W (N8)
T
JMAX
= 125
C,
JA
= 120
C/ W (S8)
S8 PART MARKING
1372
1372I
1377
1377I
1372H
1372HI
*Units shipped prior to Date Code 9552 are rated at 100
C maximum
operating temperature.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
REF
Reference Voltage
Measured at Feedback Pin
1.230
1.245
1.260
V
V
C
= 0.8V
q
1.225
1.245
1.265
V
I
FB
Feedback Input Current
V
FB
= V
REF
250
550
nA
q
900
nA
Reference Voltage Line Regulation
2.7V
V
IN
25V, V
C
= 0.8V
q
0.01
0.03
%/V
V
NFB
Negative Feedback Reference Voltage
Measured at Negative Feedback Pin
2.540
2.490
2.440
V
Feedback Pin Open, V
C
= 0.8V
q
2.570
2.490
2.410
V
I
NFB
Negative Feedback Input Current
V
NFB
= V
NFR
q
45
30
15
A
Negative Feedback Reference Voltage
2.7V
V
IN
25V, V
C
= 0.8V
q
0.01
0.05
%/V
Line Regulation
g
m
Error Amplifier Transconductance
I
C
=
25
A
1100
1500
1900
mho
q
700
2300
mho
Error Amplifier Source Current
V
FB
= V
REF
150mV, V
C
= 1.5V
q
120
200
350
A
Error Amplifier Sink Current
V
FB
= V
REF
+ 150mV, V
C
= 1.5V
q
1400
2400
A
Error Amplifier Clamp Voltage
High Clamp, V
FB
= 1V
1.70
1.95
2.30
V
Low Clamp, V
FB
= 1.5V
0.25
0.40
0.52
V
A
V
Error Amplifier Voltage Gain
500
V/ V
V
C
Pin Threshold
Duty Cycle = 0%
0.8
1
1.25
V
f
Switching Frequency
2.7V
V
IN
25V
LT1372
450
500
550
kHz
0
C
T
J
125
C
q
430
500
580
kHz
40
C
T
J
< 0
C (I Grade)
400
580
kHz
LT1377
0.90
1
1.10
MHz
0
C
T
J
125
C
q
0.86
1
1.16
MHz
40
C
T
J
< 0
C (I Grade)
0.80
1.16
MHz
ELECTRICAL C
C
HARA TERISTICS
V
IN
= 5V, V
C
= 0.6V, V
FB
= V
REF
, V
SW
, S/S and NFB pins open, unless otherwise noted.
3
LT1372/LT1377
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Maximum Switch Duty Cycle
q
90
95
%
Switch Current Limit Blanking Time
130
260
ns
BV
Output Switch Breakdown Voltage
LT1372/LT1377
q
35
47
V
LT1372HV
0
C
T
J
125
C
q
42
47
V
40
C
T
J
< 0
C (I Grade)
40
V
V
SAT
Output Switch "On" Resistance
I
SW
= 1A
q
0.5
0.8
I
LIM
Switch Current Limit
Duty Cycle = 50%
q
1.5
1.9
2.7
A
Duty Cycle = 80% (Note 1)
q
1.3
1.7
2.5
A
I
IN
Supply Current Increase During Switch On-Time
15
25
mA/A
I
SW
Control Voltage to Switch Current
2
A/V
Transconductance
Minimum Input Voltage
q
2.4
2.7
V
I
Q
Supply Current
2.7V
V
IN
25V
q
4
5.5
mA
Shutdown Supply Current
2.7V
V
IN
25V, V
S/S
0.6V
0
C
T
J
125
C
q
12
30
A
40
C
T
J
< 0
C (I Grade)
50
A
Shutdown Threshold
2.7V
V
IN
25V
q
0.6
1.3
2
V
Shutdown Delay
q
5
12
25
s
S/S Pin Input Current
0V
V
S/S
5V
q
10
15
A
Synchronization Frequency Range
LT1372
q
600
800
kHz
LT1377
q
1.2
1.6
MHz
ELECTRICAL C
C
HARA TERISTICS
V
IN
= 5V, V
C
= 0.6V, V
FB
= V
REF
, V
SW
, S/S and NFB pins open, unless otherwise noted.
Switch Saturation Voltage
vs Switch Current
TEMPERATURE (
C)
50
1.8
INPUT VOLTAGE (V)
2.0
2.2
2.4
2.6
0
50
100
150
LT1372 G03
2.8
3.0
25
25
75
125
Minimum Input Voltage
vs Temperature
DUTY CYCLE (%)
0
SWITCH CURRENT LIMIT (A)
1.0
2.0
3.0
0.5
1.5
2.5
20
40
60
80
LT1372 G02
100
10
0
30
50
70
90
25
C AND
125
C
55
C
Switch Current Limit
vs Duty Cycle
TYPICAL PERFOR
M
A
N
CE CHARACTERISTICS
U
W
SWITCH CURRENT (A)
0
SWITCH SATURATION VOLTAGE (V)
0.6
0.8
1.0
1.6
LT1372 G01
0.4
0.2
0.5
0.7
0.9
0.3
0.1
0
0.4
0.8
1.2
2.0
1.4
0.2
0.6
1.0
1.8
100
C
150
C
25
C
55
C
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1: For duty cycles (DC) between 50% and 90%, minimum
guaranteed switch current is given by I
LIM
= 0.667 (2.75 DC).
4
LT1372/LT1377
TYPICAL PERFOR
M
A
N
CE CHARACTERISTICS
U
W
Error Amplifier Output Current
vs Feedback Pin Voltage
Shutdown Delay and Threshold
vs Temperature
TEMPERATURE (
C)
50
0
SHUTDOWN DELAY (
s)
SHUTDOWN THRESHOLD (V)
2
6
8
10
20
14
0
50
75
LT1372 G04
4
16
18
12
0
0.2
0.6
0.8
1.0
2.0
1.4
0.4
1.6
1.8
1.2
25
25
100 125
150
SHUTDOWN THRESHOLD
SHUTDOWN DELAY
S/S Pin Input Current
vs Voltage
Error Amplifier Transconductance
vs Temperature
Switching Frequency
vs Feedback Pin Voltage
V
C
Pin Threshold and High
Clamp Voltage vs Temperature
FEEDBACK PIN VOLTAGE (V)
400
ERROR AMPLIFIER OUTPUT CURRENT (
A)
300
200
100
300
100
0.1
0.1
200
0
0.3
0.2
V
REF
55
C
125
C
25
C
LT1372 G06
Minimum Synchronization
Voltage vs Temperature
TEMPERATURE (
C)
50
0
MINIMUM SYNCHRONIZATION VOLTAGE (V
P-P
)
0.5
1.0
1.5
2.0
0
50
100
150
LT1372 G05
2.5
3.0
25
25
75
125
f
SYNC
= 700kHz (LT1372)
f
SYNC
= 1.4MHz (LT1377)
LT1377
LT1372
S/S PIN VOLTAGE (V)
1
S/S PIN INPUT CURRENT (
A)
1
3
5
7
LT1372 G07
1
3
0
2
4
2
4
5
1
3
5
0
8
2
4
6
9
V
IN
= 5V
FEEDBACK PIN VOLTAGE (V)
0
SWITCHING FREQUENCY (% OF TYPICAL)
70
90
110
0.8
LT1372 G08
50
30
60
80
100
40
20
10
0.2
0.4
0.6
0.1
0.9
0.3
0.5
0.7
1.0
TEMPERATURE (
C)
50
0
TRANSCONDUCTANCE (
mho)
200
600
800
1000
2000
1400
0
50
75
LT1372 G09
400
1600
1800
1200
25
25
100 125
150
g
m
=
I (V
C
)
V (FB)
TEMPERATURE (
C)
50
0.4
V
C
PIN VOLTAGE (V)
0.6
1.0
1.2
1.4
2.4
1.8
0
50
75
LT1372 G10
0.8
2.0
2.2
1.6
25
25
100 125
150
V
C
HIGH CLAMP
V
C
THRESHOLD
TEMPERATURE (
C)
50
FEEDBACK INPUT CURRENT (nA)
400
500
600
150
LT1372 G11
300
200
0
0
50
100
100
800
700
25
25
75
125
V
FB
=V
REF
Feedback Input Current
vs Temperature
TEMPERATURE (
C)
50
50
NEGATIVE FEEDBACK INPUT CURRENT (
A)
30
0
0
50
75
LT1372 G12
40
10
20
25
25
100 125
150
V
NFB
=V
NFR
Negative Feedback Input Current
vs Temperature
5
LT1372/LT1377
V
C
(Pin 1): The Compensation pin is used for frequency
compensation, current limiting and soft start. It is the
output of the error amplifier and the input of the current
comparator. Loop frequency compensation can be per-
formed with an RC network connected from the V
C
pin to
ground.
FB (Pin 2): The Feedback pin is used for positive output
voltage sensing and oscillator frequency shifting. It is the
inverting input to the error amplifier. The noninverting
input of this amplifier is internally tied to a 1.245V
reference. Load on the FB pin should not exceed 250
A
when the NFB pin is used. See Applications Information.
NFB (Pin 3): The Negative Feedback pin is used for
negative output voltage sensing. It is connected to the
inverting input of the negative feedback amplifier through
a 100k source resistor.
S/S (Pin 4): Shutdown and Synchronization Pin. The S/S
pin is logic level compatible. Shutdown is active low and
the shutdown threshold is typically 1.3V. For normal
operation, pull the S/S pin high, tie it to V
IN
or leave it
floating. To synchronize switching, drive the S/S pin be-
tween 600kHz and 800kHz (LT1372) or 1.2MHz to 1.6MHz
(LT1377).
PI
N
FU
N
CTIO
N
S
U
U
U
V
IN
(Pin 5): Bypass input supply pin with 10
F or more. The
part goes into undervoltage lockout when V
IN
drops below
2.5V. Undervoltage lockout stops switching and pulls the
V
C
pin low.
GND S (Pin 6): The ground sense pin is a "clean" ground.
The internal reference, error amplifier and negative feed-
back amplifier are referred to the ground sense pin. Con-
nect it to ground. Keep the ground path connection to the
output resistor divider and the V
C
compensation network
free of large ground currents.
GND (Pin 7): The ground pin is the emitter connection of
the power switch and has large currents flowing through it.
It should be connected directly to a good quality ground
plane.
V
SW
(Pin 8): The switch pin is the collector of the power
switch and has large currents flowing through it. Keep the
traces to the switching components as short as possible to
minimize radiation and voltage spikes.
+
NFBA
NFB
S/S
FB
100k
50k
0.08
+
EA
V
C
V
IN
GND
LT1372 BD
GND SENSE
1.245V
REF
5:1 FREQUENCY
SHIFT
OSC
SYNC
SHUTDOWN
DELAY AND RESET
LOW DROPOUT
2.3V REG
ANTI-SAT
LOGIC
DRIVER
SW
SWITCH
+
IA
A
V
6
COMP
BLOCK DIAGRA
M
W
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